1. Field of the Invention
The present invention concerns a product for topical application which is capable of releasing a cosmetic and/or dermatological active ingredient on the skin and its use in the cosmetic and/or dermatological treatment of the skin, including the scalp.
2. Discussion of the Background
It is known to introduce active ingredients into cosmetic and/or dermatological compositions for the purpose of contributing specific treatments to the skin, for example in combating drying, aging or pigmentation of the skin, for treating acne or certain skin diseases (eczema, psoriasis), for combating excess weight, for promoting restructuring of the skin or its cell renewal, and for dyeing the skin.
For example, ascorbic acid (or vitamin C) is known for stimulating the growth of connective tissue, especially collagen. It also makes it possible to reinforce the defenses of cutaneous tissue against external attacks, such as ultraviolet radiation or pollution. It is also used for removing stains and pigmentation from the skin, and also for promoting healing of the skin.
Application of retinol or vitamin A makes it possible to combat in particular cutaneous aging and to combat certain skin disorders, such as acne or disorders of keratinization or of healing.
In addition, tocopherols, such as vitamin E, are known to have antioxidizing properties with respect to phospholipids of the cell membrane and properties in counteracting free radicals (see "Radicaux libres et Vitamine E Free radicals and vitamin E!" by J. B. Chazan and M. Szulc--Cah. Nutr. Diet., 1987, 6, XXII, 1, pages 66 to 76).
Moreover, application of dihydroxyacetone to the skin makes it possible to provide the appearance of a suntan on the skin, without the disadvantages (burns, cancer risk) encountered during exposure to the sun.
Unfortunately, certain active ingredients, and in particular those mentioned above, are unstable and are sensitive to external factors such as light or heat. This instability goes against the desired effectiveness and can, moreover, be a source of annoyance to the user, for example when the instability of the active ingredient leads to modifications in the color and/or smell of the composition containing it.
Consequently, various means have been envisaged for stabilizing these active ingredients. For example, one such means involves blocking the reactive site of the active ingredient by esterification, in particular with phosphate, sulphate or alkyl derivatives, and in using the derivatives in place of the free active ingredient. Unfortunately, the derivatives are not as effective as the free active ingredient.
It has also been envisaged to use precursors of such active ingredients, which, after application to the skin, are converted by cutaneous enzymes to the free active ingredient. For example, European patent publication No. EP-A-487,404 discloses the use of a glucosylated derivative of ascorbic acid in dermatological compositions which is easily hydrolysed by cutaneous enzymes and thus capable of releasing ascorbic acid when these compositions are applied to the skin. However, the use of such derivatives does not make possible rapid release, in a sufficient amount, of ascorbic acid at the surface of the skin.
Thus, there remains the need for products for topical application containing cosmetic and/or dermatological active ingredients in which the active ingredients retain their properties and effectiveness with time.